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| Reports on Overseas' Conferences and Meetings |
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Report on the15th International Symposium on Microdosimetry,
MICROS2009 |
| Keiji Suzuki, Department of Molecular Medicine |
MICROS2009, 15th International Symposium on Microdosimetry, was held in Verona, Italy, between October 25th and 30th. This symposium was aimed to understand the initial physical process, which deposits radiation energy to DNA molecules, and to model the process, by which DNA damage gives rise to radiation effetcs. Because the initial physical process is tightly related to the production of DNA double strand breaks, biological studies on DNA damage are indispensable for microdosimetry. Therefore, it was an interdisciplinary symposium involving physicists, biologists, and modelistes.
It is well known that radiation effects are very much affected by the radiation quality. For example, high-LET radiation is more effective than low-LET radiation per unit dose. This is because high-LET radiation induces high density ionization along the track, whereas low-LET radiation causes spares ionization. Thus, such difference in the so called "track structure" is the most critical factor to determine the biological effects. And, this is the reason why microdosimetry is needed to estimate the effect of radiation. Because there are still many uncertainties left in the effects of low dose ionizing radiation, microdosimetrical simulation is expected to solve these problems. Furthermore, medical usage of high-LET radiation, heavy ion particles in the space flight, and growing number of atomic power plants made it urgent to simulate the effects of high-LET radiation in order to estimate risks from such radiation.
It was really my surprise that recent advances in the research of chromatin structure made amazing progress in the simulation of track structure by the Monte Carlo equation. There were several simulation codes corresponding to the radiation quality. None of them were still perfect, but, simulation was greatly improved if the radiation quality is defined. Especially, clustered damage, which is predominantly induced by high-LET radiation, can now been simulated in some extent. DNA double strand breaks, caused by direct deposition of the radiation energy, were simulated together with those generated by two independent breaks induced in opposite strands. Such simulation further extend the modeling of not only the induction kinetics of clustered damage but also slow repair of them. Thus, even the clustered damage was now modeled in part.
As we discussed in the symposium, current simulation codes were still not enough to model complex process of induction and repair of DNA damage caused by high-LET radiation. Further information was requited from the side of biologists. Especially, to connect microdosimetry with risk estimation needs more basic mechanisms that explain delayed effects of radiation. For example, the bystander effects, which are well known non-targeted effects induced after irradiation, have not been explained with the detailed molecular mechanisms. Thus, it is quite evident that we need more researches towards the comprehensive understandings of the radiation effects. One such clue must be a systems radiation biology. A couple of laboratories have already started the initial process, which unites a team consisting different experts. Although the final goal of systems radiation biology is obscure, it definitely be one way to pursue. As it is quite evident that systems radiation biology needs international collaboration, Nagasaki Global COE program may provide an unique opportunity to do this in the framework of an international consortium of radiation biology. Together with the international low dose program, our program should contribute to the better understandings of the low dose effects on human beings. |
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